This invention relates to compositions of matter classified in the art of chemistry as laminated structures (laminates) of fluoropolymers and high temperature formable polymers, more particularly laminated structures of polyvinylidene fluoride and high temperature formable polymers selected from the group consisting of polyetherimide, polyethersulfone, polyphenylene sulfide and polyetheretherketone polymers, processes for the preparation and use of such laminates, as well as to formed products produced from the laminates.
Sheets of thermoplastic polymers may be classified in two major categories, those that can be thermoformed at low to moderate temperatures, up to 475.degree. F. (246.degree. C.), and those thermoformable at significantly higher temperature, from about 500.degree. F. (260.degree. C.) up to about 600.degree. F. (316.degree. C.). The former category includes polycarbonate, acrylic, polyvinyl chloride, chlorinated polyvinyl chloride and polyetherketoneketone sheet. The latter category includes polyetherimide, polyether sulfone, polyphenylene sulfide and polyetheretherketone sheet. Those sheets in the lower temperature category can be finished in three ways. They can be internally pigmented to achieve a desired color; the surface can be laminated with either a pigmented or clear film; and they can be painted. In fact, all three methods are utilized. Laminating with films is especially desirable in a number of applications, such as surface transportation, aircraft interiors and clean room enclosures, because the films provide greatly enhanced decorative and performance properties to the finished part. These properties include greater color control, improved color stability, improved cleanability and greater abrasion resistance. Because no suitable materials had been identified for forming laminates, only internal pigmentation and painting have been available for sheets in the higher temperature category. Since the introduction of these higher temperature sheets over the last 10 or 15 years, technicians in the applicable industries have sought a decorative film which can stand up to the high thermoforming temperatures these sheets must reach in order that a part will attain satisfactory geometry.
There are at least four types of decorative films used by thermoplastic sheet manufacturers for thermoforming at lower temperatures. These are polyvinyl fluoride films, acrylic films, polyvinyl chloride films and polyvinylidene fluoride-based films. With the polyvinyl fluoride, polyvinyl chloride, and acrylic films, it is well known that their upper use temperature limit is about 400.degree. F. (205.degree. C.), beyond which the films begin to disintegrate. The maximum use temperatures for polyvinylidene fluoride-based films had not been determined although the melting points, depending on the copolymer used, are known to be somewhat below 340.degree. F. (170.degree. C.) and lower. Nevertheless, it has been found that polyvinylidene fluoride films can survive intact through the high forming temperatures used in molding parts from high temperature formable polymer sheets.
Thus, sheet manufacturers can now use a film laminate with improved decorative and performance characteristics while also avoiding the problems such as environmental damage involved in painting of formed parts.
The polyvinylidene fluoride film is produced either from melted polymer or on equipment where solvents are controlled either by solvent recovery or by incineration. Many thermoformers, on the other hand, are poorly equipped to handle the solvents evaporated from paints and many operate under governmentally imposed restrictions on emission of solvents greater than present limits.